1. Field of the Invention.
This invention relates in general to spindle motors for use in magnetic disk storage systems, and more particularly to a method and apparatus for replenishing oil in a fluid dynamic bearing using a sleeve groove.
2. Description of Related Art.
The storage capacity and general performance of hard disk drives have improved steadily over the last decade in response to the increasing demands of the computer industry. These developments have been mainly fueled by corresponding advances in the components of magnetic recording technology and in electronic sophistication and miniaturization. In particular, magnetic read/write recording heads and disks are capable of supporting a real data storage densities typically ten times greater than they could ten years ago. This is being achieved by higher track densities, higher linear flux transition densities and lower recording head flying heights.
Data storage systems, such as disk drives, commonly make use of rotating storage disks. The storage disks are commonly magnetic disks but could also be optical. In a typical magnetic disk drive, a magnetic disk rotates at high speed and a transducing head uses air pressure to xe2x80x9cflyxe2x80x9d over the top surface of the disk. The transducing head records information on the disk surface by impressing a magnetic field on the disk. Information is read back using the head by detecting magnetization of the disk surface. The magnetic disk surface is divided in a plurality of concentric tracks. By moving the transducing head radially across the surface of the disk, the transducing head can read information from or write information to different tracks of the magnetic disk.
The recording medium, i.e., magnetic disk, holds information encoded in the form of magnetic transitions. The information capacity, or areal density, of the medium is determined by the transducer""s ability to sense and write distinguishable transitions. An important factor affecting areal density is the distance between the transducer and the recording surface, referred to as the fly height. It is desirable to fly the transducer very close to the medium to enhance transition detection. Some fly height stability is achieved with proper suspension loading and by shaping the air bearing slider surface (ABS) for desirable aerodynamic characteristics.
Spindle motors are commonly used to rotate magnetic disks at high speeds. Frequently, conventional spindle motors comprise small electric motors equipped with standard bail bearings. However, electric motors having ball bearings are known to experience problems such as runout or vibration that can prevent information from being accessed from disks rotated by the motors. This is especially true as advancements in data storage technology have increased magnetic disk storage densities.
The point is now being reached, however, where further advances are likely to be impeded by mechanical constraints. In particular, limitations will result from the spindle hub holding the stack of disks on account of the properties of the ball bearing assemblies used for rotational support. Random vibrations in both axial and radial axes ultimately lead to limitations in positioning accuracies and signal-to-noise ratios with consequences for storage capacities. The radial accuracy directly limits the number of concentric tracks on a disk on which data can be stored and reliably retrieved.
To overcome the problems associated with ball bearing electric motors, some disk drive systems now make use of electric motors having fluid hydrodynamic bearings. Bearings of this type are shown in U.S. Pat. Nos. 5,427,546 to Hensel, 5,516,212 to Titcomb and 5,707,154 to Ichiyama.
An exemplary hydrodynamic bearing typically includes a stationary shaft on which is mounted a rotary hub to which magnetic disks can be secured. There is no direct contact between the rotating hub and the shaft. Instead, a lubricating fluid such as air or oil forms a hydrodynamic bearing between the shaft and the rotary hub. Hydrodynamic pressure causes the lubricating fluid to act as a bearing between the shaft and the rotary hub. Frequently, capillary seals are used to retain the bearing fluid between the shaft and the rotary hub.
When used in association with spindle motors, air bearings provide numerous advantages. For example, air bearings are more efficient and consume less power than either ball bearings or oil bearings. Also, air bearings are quiet and have excellent run out characteristics.
Still, oil bearings have some disadvantages. For example, oil bearings consume more power than ball bearings or air bearings. Furthermore, when oil bearings are used in the journal bearing environment, oil leakage can be problematic.
In the future, spindle motor disk rotation speeds will steadily increase. As disk rotation speeds increase, the problems associated with standard oil bearings, air bearings and ball bearings will become magnified. Increased disk recording density is another trend in the industry. The combination of increased disk rotation speeds and increased recording densities will require disk drives to operate with improved run out characteristics. Thus, air bearings will be used more frequently as the rotating speed is increased because of the above-mentioned advantages.
However, to become more reliable, the problem with fluid leakage must be overcome. Presently, there is no known replenishment system that guarantees the oil will be returned at controllable rate.
It can be seen then that there is a need for a method and apparatus for replenishing oil in a fluid dynamic bearing using a sleeve groove.
To overcome the limitations in the prior art described above, and to overcome other limitations that will become apparent upon reading and understanding the present specification, the present invention discloses a method and apparatus for replenishing oil in a fluid dynamic bearing using a sleeve groove.
The present invention solves the above-described problems by providing a replenishing groove in the sleeve surrounding the shaft that centrifugal force forces the oil to move toward the radial bearings.
A sleeve in accordance with the principles of the present invention includes a cylindrical member having a bearing surface and at least one groove formed in the bearing surface of the cylindrical member extending from the center of the cylindrical member to at least one end of the cylindrical member, the groove defining a channel for directing the flow of oil to the at least one end of the cylindrical member.
Other embodiments of a sleeve in accordance with the principles of the invention may include alternative or optional additional aspects. One such aspect of the present invention is that the at least one groove comprises a plurality of grooves dispersed at predetermined positions along an inner circumference of the bearing surface.
Another aspect of the present invention is that the groove extends in the bearing surface from the center of the cylindrical member to a top and bottom of the cylindrical member.
Another aspect of the present invention is that the groove increases in depth as the groove extends toward at least one end of the cylindrical member.
Another aspect of the present invention is that the groove becomes wider as the groove extends toward at least one end of the cylindrical member.
In another embodiment of the present invention, a disk drive is provided. The disk drive includes at least one disk for recording and reading data thereon, a motor, coupled to the at least one disk, for rotating the at least one disk, at least one head disposed proximate the at least one disk for writing and reading data to and from the at least-one disk and an actuator arm assembly, coupled to the at least one head, for moving the at least one head relative to the at least one disk, wherein the motor further comprises a fluid dynamic bearing having a sleeve, the sleeve of the fluid dynamic bearing further including a cylindrical member having a bearing surface and at least one groove formed in the bearing surface of the cylindrical member extending from the center of the cylindrical member to at least one end of the cylindrical member, the groove defining a channel for directing the flow of oil to the at least one end of the cylindrical member.
In another embodiment of the present invention, a fluid dynamic bearing system is provided. The fluid dynamic bearing system includes a rotating shaft, an upper radial bearing for supporting the shaft at an upper end, a lower radial bearing for supporting the shaft at a lower end, a sleeve disposed around the upper and lower radial bearings and the shaft, the sleeve forming a chamber between the upper and lower radial bearings, wherein the chamber collects oil leaking from the upper radial bearing and the lower radial bearing and wherein the sleeve further includes a cylindrical member having a bearing surface and at least one groove formed in the bearing surface of the cylindrical member extending from the center of the cylindrical member to at least one end of the cylindrical member, the groove defining a channel for directing the flow of oil to the at least one end of the cylindrical member for replenishing at least one of the upper and lower radial bearings.
In another embodiment of the present invention, a method for replenishing oil to a fluid dynamic bearing is provided. The method includes forming a cylindrical member having a bearing surface, forming at least one groove in the bearing surface of the cylindrical member extending from the center of the cylindrical member to at least one end of the cylindrical member, and driving oil through the groove to the at least one end of the cylindrical member.
Another aspect of the present invention is that the forming at least one groove further comprises forming a plurality of grooves dispersed at predetermined positions along an inner circumference of the bearing surface.
Another aspect of the present invention is that the forming at least one groove further comprises forming a groove in the bearing surface extending from the center of the cylindrical member to a top and bottom of the cylindrical member.
Another aspect of the present invention is that the forming at least one groove further comprises forming a groove that increases in depth as the groove extends toward at least one end of the cylindrical member.
Another aspect of the present invention is that the forming at least one groove further comprises forming a groove that becomes wider as the groove extends toward at least one end of the cylindrical member.
These and various other advantages and features of novelty, which characterize the invention, are pointed out with particularity in the claims annexed hereto and form a part hereof. However, for a better understanding of the invention, its advantages, and the objects obtained by its use, reference should be made to the drawings which form a further part hereof, and to accompanying descriptive matter, in which there are illustrated and described specific examples of an apparatus in accordance with the invention.